6.
Joe Biden

At this point, the only way Vice President Biden gets into the race is if something happens to Hillary Clinton. But there’s no doubt that Biden would have liked to run for president again, if the circumstances were right.

For years, Mr. Biden dropped hints about 2016. On Election Day 2012, while waiting in line to vote in his home state of Delaware, he was asked if this was the last time he’ll vote for himself. He smiled: “No, I don’t think so.” At another point he joked about running for “county council or something.”

In July 2013, Biden told GQ magazine: "I can die a happy man never having been president of the United States of America. But it doesn't mean I won't run."

Age might be an issue. Biden will be in his mid-70s in 2016. If he runs, he’d be angling to be the oldest person ever elected president.

Biden has been a Washington fixture since his first election to the Senate in 1972 – and he’s run for president twice before.